1. Field of the Invention
The present invention relates to a method of simulating short depth of field and digital camera using the same, and more particularly, to a method of simulating short depth of field and digital camera utilizing digital processing method to sharpen objects close to a focus and blur object far from the focus.
2. Description of the Prior Art
In general, a lens can only precisely focus the light on a spot with a certain distance, and thus the sharpness of an image of an object decreases gradually away from each side of the spot. Depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image for eyesight, so within the DOF, the unsharpness is imperceptible under normal viewing conditions.
Usually, consumer digital cameras have small aperture and long depth of field to make the entire image sharp, but the focused object can not be emphasized. On the contrary, single lens cameras have large aperture and short depth of field to sharp the focused object and blur the non-focused object, so as to emphasize the desirable object.
For example, please refer to FIG. 1, which is a schematic diagram of conventional image formations with a large aperture lens Len1 and a small aperture lens Len2, respectively. As shown in FIG. 1, the large aperture lens Len1 is designed for focusing light from an object 2a with an object distance D2 precisely on a film 100 to form an image 2a′, and the small aperture lens Len2 is designed for focusing light from an object 2b with the object distance D2 precisely on an image sensor 102 to form an image 2b′, wherein the image sensor 102 can be a charge coupled device (CCD) sensor or other image sensors. As can be seen from FIG. 1, light from objects 1a and 3a with an object distance D1 can not be precisely focused on the film 100, light from objects 1b and 3b with an object distance D3 can not be precisely focused on the image sensor 102 either, so the large aperture lens Len1 forms blurrier images 1a′ and 3a′ due to short depth of field, while the small aperture lens Len2 forms sharper images 1b′ and 3b′ due to long depth of field. Noticeably, the prior art changes an object distance with which light from an object can be precisely focused by moving the large aperture lens Len1 and the small aperture lens Len2.
Therefore, conventional digital cameras or camera phones usually utilize image processing to blur part of the image captured by the sensor 102 to emphasize a specific object. For example, in the conventional touch camera phones, users may touch the touch screen to define the object for emphasis, and then the touch camera phone can blur the image by a radial blur mode, that is, sharpness of the image is highest on the touched point and gradually decreases as distancing from the touched point. Or, users may select a horizontal line, and the touch camera phone blurs the image by a horizontal blur mode, i.e. sharpness of the image is highest on the horizontal line and decreases as distancing from the horizontal line.
However, the method of the conventional image processing is to blur part of the image within a certain region or by certain blur modes, and thus the sharpness of images of objects with a same object distance from the digital camera may be different after image processing, and the processed image has a lower quality compared with the image captured by a single lens camera with short depth of field. Besides, a lens with large aperture is manufactured with high cost, and thus not suitable for the consumer digital camera.
Moreover, the prior art can also simulate short depth of field by capturing two images, wherein one of the images is focused on a foreground and the other is focused on a background. Then, the conventional method separates the foreground image and the background image by image processing, and blurs the background image and blends the foreground image with the blurred background image through image processing techniques, such that the object in the foreground is emphasized and the background is de-emphasized. However, it needs to shoot two images for alignment before simulating short depth of field, which increases complexity. Besides, there are only two blurring levels in the image, i.e. the foreground image and the background image, which can not precisely present sense of distance.
According to mentioned disadvantages, there is a need to improve the prior art to utilize better image blurry method for simulating short depth of field image.